Ricerca del bosone di Higgs nel canale di decadimento $H \to ZZ^{(*)}\to l^+l^-q \overline{q} $ nell'esperimento ATLAS ad LHC

The search for a Standard Model Higgs boson in the channel $H\to ZZ \to l^{+} l^{-} q\overline{q}$ ($\ell=e,\mu$) using $4.7 fb^{-1}$ of $pp$ collisions data collected by the ATLAS experiment at $\sqrt{s}=7$ TeV is presented in the full mass range. The signature for signal events is given by two same flavor leptons and two jets coming from hadronic decay of the Z and thus mainly composed of quark generated-jets. This decay channel suffers a huge background contamination coming mainly from the Z+jets and Drell-Yan processes both giving a large contribution coming from gluon-jets. Aiming the improvement of the sensitivity for the $H\to ZZ \to l^{+} l^{-} q\overline{q}$ decay channel a tool designed to separate quark-initiated jets from gluon-initiated jets has been developed. The development and impact on the analysis of a multivariate discriminant for the quark-gluon tagging is shown.